Cannabis can help shrink tumours in cancer patients, scientists have found.

New research reveals the drug’s main psychoactive ingredient - tetrahydrocannabino (THC) - may be responsible for its success in reducing tumours.

It is hoped the findings will help develop a synthetic equivalent with anti-cancer properties.

More than 330,000 people in the UK are diagnosed with cancer every year.

But researchers today warned that cancer sufferers should not be tempted to self-medicate.

Dr Peter McCormick, of the University of East Anglia’s (UEA) school of pharmacy, said THC’s anti-cancer properties had been known but the study identified the receptors responsible for fighting tumours.

He added: “Our findings help explain some of the well-known but still poorly understood effects of THC at low and high doses on tumour growth.

“There has been a great deal of interest in understanding the molecular mechanisms behind how marijuana, and specifically THC, influence cancer pathology.

“There has also been a drive in the pharmaceutical industry to create synthetic equivalents that might have anti-cancer properties.

“By identifying the receptors involved we have provided an important step towards the future development of therapeutics that can take advantage of the interactions we have discovered to reduce tumour growth.”

The research, carried out with the Universidad Complutense de Madrid in Spain, used samples of human breast cancer cells to induce tumours in mice.

They then targeted the tumours with doses of the cannabis compound and found that two cell receptors in particular were responsible for the drug’s anti-tumour effects.

Dr McCormick said: “Our research uses an isolated chemical compound and using the correct concentration is vital.

“Cancer patients should not use cannabis to self-medicate, but I hope that our research will lead to a safe synthetic equivalent being available in the future.”